Fig. 6. Tumour cells stimulate release of self-activating factors in endothelial cells. (A) Schematics of transfer experiments. HUVECs were cultivated in the inserts of Transwell chambers in EBM-2 medium alone as acceptor cells and were also used as negative controls. HUVECs were also co-cultivated with HUVECs (naive HUVECs) in both compartments or with U87 cells in inserts (activated HUVECs). Inserts were discarded and cells in the bottom compartment were intensively washed and co-incubated with acceptor cells for 24 hours. (B) Increase in formation of net-like structures by acceptor cells co-cultivated with naive or activated HUVECs. Net-like structures were quantified as described in Materials and Methods and shown in Fig. 2. Significance was estimated by unpaired Student's t-test. (C) Stimulation of RANTES and FGF7 production by HUVECs activated by tumour-conditioned medium. U87 cells and HUVECs were set up in T150 flasks and treated as described in Materials and Methods. HUVEC-conditioned medium is indicated as HCM and tumour-conditioned medium as TCM. The concentrations are shown in pg ml^–1 of FGF7 and RANTES in HUVEC+HCM culture medium (open bars, –FGF7; dashed bars, –RANTES) and in HUVEC+TCM culture medium (grey bars, –FGF7; black bars, –RANTES). Error bars are standard deviations.